Conjugate fibers having an optical interference color-generating function, composed of mutually independent polymer layers with different refractive indices forming an alternating laminate, produce interference coloring of wavelengths in the visible light region due to the reflection and interference effects of natural light. The color development has a brightness with a metallic gloss, and produces a pure and clear color (monochromatic) with a specific wavelength, while exhibiting an aesthetic quality entirely different from color formed by the light absorption of a dye or pigment. A concrete example of a conjugate fiber having an optical interference color-generating function is disclosed in International Patent Publication No. WO98/46815.
However, when it is attempted to increase the fineness of the conjugate fiber having an optical interference color-generating function as disclosed in the aforementioned international patent publication, peeling of the alternate laminated layers may occur, or even when peeling does not occur the spinning condition may be impaired due to degradation of the polymer during spinning or the optical interference effect may be reduced by unevenness produced during the drawing step; this has constituted an impediment against development of the fiber to product applications which require improved aesthetic qualities, particularly for paints which must have a fine fiber size, cut fibers for such purposes as cosmetics and printing, and even for some filament uses.